# Specific Absorption Ratio (SAR) and its Measurement in Smart Phone

SAR is a measure of the rate of RF energy absorption by the body from the source being measured. It is defined as the power absorbed per mass of tissue and has units of watts per kilogram (W/kg). SAR is usually averaged either over the whole body, or over a small sample volume (typically 1 g or 10 g of tissue).

SAR Testing

To test cell phones for SAR compliance, the phone is precisely placed in various common positions next to the head and body, and a robotic probe takes a series of measurements of the electric field at specific pinpoint locations in a very precise, grid-like pattern within the dummy head and torso. Only the highest SAR values for each frequency band are included in the final authorization to demonstrate compliance with the FCC’s RF guidelines.

SAR is measured in three ways:

• Whole body average, which is the total amount of energy dissipated in the human body, expressed as an average of the total mass of the human body
• 10g cube localized peak, which is the highest level of energy dissipation in any 10g cube of tissue in the human body
• 1g cube localized peak, which is the highest level of energy dissipation in any 1g cube of tissue in the human body

SAR Calculation

SAR Testing is done to meet requirements in ANSI/IEEE C95.3: 2002: “IEEE Recommended Practice for Measurements and Computations of Radio Frequency Electromagnetic Fields With Respect to Human Exposure to Such Fields, 100 kHz–300 GHz” which defines procedures for SAR averaging for “Body” and “Extremities

SAR=(σ|E_x |^2)/2ρ+(σ|E_y |^2)/2ρ+(σ|E_z |^2)/2ρ

• SAR = Specific Absorption Rate (Watts/kg)
• σ= Electrical conductivity
• |Magnitude of the Electric Field (Volts/m)
• = Material Density (kg/m3)